LM5034 datasheet(13/36 Pages) TI

13 / 36 page

Drivers Off

UVLO

Disable

UVLO

7.6V/6.2 V

THERMAL

SHUTDOWN

Max

. Duty

Cycle Limiter

20 PA

LM5034

VPWR

VCC

1.25V

LM5034

www.ti.com

SNVS347A – FEBRUARY 2005 – REVISED APRIL 2013

Figure 20. Drivers Off and VCC Disable

Startup Regulator, VIN, VCC1, VCC2

The high voltage startup regulator is integral to the LM5034. The input pin VIN can be connected directly to a

voltage between 13V and 100V, with transient capability to 105V. The startup regulator provides bias voltages to

the series pass VCC regulator and the UVLO circuit. The VCC regulator is disabled until the voltage at the UVLO

pin (described above) exceeds 1.25V. For applications where VPWR exceeds 100V the internal startup regulator

can be powered from an external startup regulator or other available low voltage source. See Applications

Information for details.

The VCC under-voltage threshold circuit (UVT) monitors the VCC regulator output. When the series pass

regulator is enabled and the internal VCC voltage increases to > 7.6V, the UVT comparator activates the PWM

controller and output drivers via the Drivers Off signal. The UVT comparator has built-in hysteresis, with the lower

threshold nominally set to 6.2V. See Figure 5 and Figure 20.

When enabled, the VCC regulated output is 7.7V ±4% with current limited to a minimum of 19 mA (typically 22

mA). The regulator’s output is split by a resistor divider to provide separate VCC1 and VCC2 rails for the two

controller channels. VCC1 powers Controller 1, drivers OUT1 and AC1, Soft-start1, and all the support functions.

VCC2 powers Controller 2, drivers OUT2 and AC2, and Soft-start2. If VCC1 and/or VCC2 are used to power

external circuitry, the current limit specification applies to the sum of the load currents at the two pins.

Splitting the VCC regulator output through two 5Ω resistors allows separate external VCC bypass capacitors to

reduce cross-talk between channels. Each VCC output pin requires a capacitor to its corresponding ground for

stability, as well as to provide the surge currents to the external MOSFETs via the gate driver outputs. The

capacitors should be the same value, and be physically close to their respective pins.

In most applications it is necessary to power VCC from an external source as the average current required at the

output drivers may exceed the current capability of the internal regulator and/or the thermal capability of the

LM5034 package (see Figure 8). Normally the external source is derived from the converter’s power stage once

the LM5034 outputs are active. See Applications Information for more information.

Drivers Off, VCC Disable

Referring to Figure 20, Drivers Off and VCC Disable are internal signals which, when active disable portions of the

LM5034. If the UVLO pin is below 1.25V, or if the thermal shutdown activates, the VCC Disable line switches high

to disable the VCC regulator. UVLO also activates the Drivers Off signal to disable the output drivers, connect the

SS1, SS2, COMP1, COMP2 and RES pins to ground, and enable the 50 µA Soft-start current sources.

If the VCC voltage falls below the under-voltage threshold of 6.2V , the UVT comparator activates only the Drivers

Off signal. The output drivers are disabled but the VCC regulator is not disabled. Additionally, the CS1, CS2, SS1,

SS2, COMP1, COMP2 and RES pins are internally grounded, and the 50 µA Soft-start current sources are

enabled.

Submit Documentation Feedback

Product Folder Links: LM5034

LM5034 Datenblatt(PDF) 13 Page - Texas Instruments

LM5034 Datenblatt(HTML) 13 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Datenblatt Download

Link URL